All of the following are regulating enzymes of glycolysis, except
**Core Concept**
The regulation of glycolysis involves a complex interplay of enzymes and covalent modifications to control the flow of glucose through the glycolytic pathway. Key enzymes in this regulation include hexokinase/glucokinase, phosphofructokinase-1 (PFK-1), and pyruvate kinase (PK).
**Why the Correct Answer is Right**
Phosphoglucose isomerase is a glycolytic enzyme that catalyzes the conversion of glucose-6-phosphate to fructose-6-phosphate. However, it is not typically considered a regulatory enzyme of glycolysis. In contrast, hexokinase/glucokinase, PFK-1, and pyruvate kinase are all key regulatory enzymes of glycolysis. Hexokinase/glucokinase is the first committed step in glycolysis, PFK-1 is a key allosteric regulatory enzyme, and pyruvate kinase is a key enzyme in the final step of glycolysis.
**Why Each Wrong Option is Incorrect**
**Option A:** Hexokinase/glucokinase is a regulatory enzyme of glycolysis, as it is the first committed step and has a high Km for glucose, allowing for allosteric regulation.
**Option B:** Phosphofructokinase-1 (PFK-1) is a key regulatory enzyme of glycolysis, as it is allosterically inhibited by high ATP and citrate levels, and activated by low ATP and high ADP levels.
**Option C:** Pyruvate kinase is a key regulatory enzyme of glycolysis, as it is allosterically inhibited by high ATP and citrate levels, and activated by low ATP and high ADP levels.
**Clinical Pearl / High-Yield Fact**
A key clinical correlation is that the regulation of glycolysis is often disrupted in cancer cells, leading to the upregulation of glycolytic enzymes and the reliance on glycolysis for energy production, even in the presence of oxygen. This phenomenon is known as the Warburg effect.
**Correct Answer: A. Phosphoglucose isomerase.**